1. Field of the Invention
The present invention relates to a plasma processing apparatus and, more particularly, to an inductively coupled plasma processing apparatus.
2. Description of the Related Art
An inductively coupled plasma processing apparatus comprises a vacuum chamber in which a workpiece to be processed is placed on a susceptor and a high frequency induction antenna that is placed outside of the chamber in the atmosphere. When gas is supplied into the vacuum chamber and at the same time an electromagnetic field generated by currents through the induction antenna is applied to the gas, the gas is ionized or becomes a gas plasma. The gas plasma is used for deposition or etching processes on the workpiece such as a semiconductor wafer, or a glass substrate, to be processed.
Conventionally a plate such as a wall or a part of the wall that separates the induction antenna from the vacuum chamber was made of dielectric material plate in order to effectively produce an electromagnetic field in the vacuum chamber. Therefore, when the plasma is produced, a high voltage is applied between both sides of the dielectric material plate. A surface of the dielectric material plate that faces the vacuum chamber is hit by ions that are accelerated by the high voltage. The dielectric material plate is damaged through the ion attack. The ions can sputter the dielectric material plate and unwanted contaminations can be produced.
In recent years it has been necessary to use a large vacuum chamber and induction antenna in order to extend the area of the plasma for large workpieces. The dielectric material plate also became larger. It is difficult to make such a large dielectric material plate because the large dielectric material plate is fragile.